Myoclonus

Myoclonus is defined as sudden, brief, jerky, shocklike, involuntary movements involving the extremities, face, and trunk, without loss of consciousness. Myoclonus is one of the most commonly encountered involuntary movements, and it can be seen in association with a variety of conditions. This review covers  the epidemiology, classification, and diagnosis of myoclonus, as well as a thorough discussion of cortical myoclonus, myoclonus of brainstem origin, myoclonus of spinal cord origin, and myoclonus of undetermined origin. Figures show the principle of jerk-locked back-averaging, example data of jerk-lock averaging, schematic diagrams of cortical reflex myoclonus and spontaneous cortical myoclonus, a polygraphic electromyogram (EMG) recorded from a patient with postanoxic, reticular reflex myoclonus, surface negative slow electroencephalographic (EEG) potentials recorded before psychogenic jerks and voluntary movements mimicking the jerks in a patient with a diagnosis of psychogenic truncal movements, and an EEG-EMG polygraph in a patient with Creutzfeldt-Jakob disease. Tables list the classification of myoclonus based on the estimated site of origin, causes of cortical myoclonus, and causes of progressive myoclonus epilepsy and gene abnormalities.   Key words: cortical myoclonus, EEG-EMG polygraph, epilepsy syndromes, involuntary movements, myoclonus   This review contains 6 highly rendered figures, 3 tables, and 63 references.